Thermal hysteresis in ganglioside micelles investigated by differential scanning calorimetry and light-scattering

Both light-scattering and differential scanning calorimetry (DSC) measureme nts account for the existence of a dramatic thermal hysteresis effect occur ring in micellar solutions of gangliosides. Light-scattering measurements r eveal that the mean aggregation number of ganglioside micelles assumes diff erent values depending on the sample thermal history, a hysteresis phenomen on that completely disappears above a well-defined temperature. On the othe r side, DSC measurements assess that the heat-capacity variation versus tem perature for the ganglioside micellar system depends as well on the thermal history of the sample. Although rather complicated, the calorigrams show a peak associated with the melting of the micelle hydrophobic core. The posi tion of the peak undergoes changes consistent with the observed hysteresis of the mean aggregation number. The two parallel descriptions, geometric an d calorimetric, can be clearly correlated as two aspects of the same phenom enon and give support to each other. The hysteresis behavior below a critic al temperature is related to cooperative conformational variations of the o ligosaccharide headgroup at the micellar surface. Such surface phenomena ar e coupled to the well-known order-disorder transition of the hydrophobic ch ains in the core via the geometric constraints imposed by the confinement o f the amphiphiles in the micellar aggregate.